A liquid crystal panel driver LSI and a CCD driver LSI, for example, are operated at a power supply voltage of 10V or higher, and therefore high breakdown voltage transistors having a breakdown voltage of 20V or higher are normally required. On the other hand, low breakdown voltage transistors are used in internal control logic sections that need to be small in size and high speed. Wells where high breakdown voltage transistors are formed need to be made deeper in order to secure the well breakdown voltage. In contrast, wells where low breakdown voltage transistors are formed tend to be made shallower in order to reduce the element size and to achieve higher speeds. For this reason, high breakdown voltage transistors are formed in a chip that is different from a chip for low breakdown voltage transistors, and are known to be formed as an externally mounted circuit.